The widespread availability of bench-top optical imaging systems for use with small animals and cell cultures has resulted in the rapid growth of research involving bioluminescent and fluorescent labels (Graves 2004; Ntziachristos 2006; Klose 2009; Leblond 2010). Laboratory optical imaging systems provide rapid, routine quantitative measurements of light intensity, facilitating comparison of the uptake and expression of optical labels. While these systems often provide values in quantitative units of radiance or intensity, there is often no means for routine quality assurance (Resch-Genger 2005; Sevick-Muraca 2013). This makes it difficult to compare values between different systems, or to maintain confidence in reported values following maintenance or system upgrades. It can also be challenging to ensure that light intensity values are being reported accurately over different fields of view or acquisition parameters.
Specialized calibration and monitoring devices have been previously described (Troy 2004; Nelson 2005; Esmonde-White 2011; Vonwil 2014; Bentz 2016), but no routine solution is available for monitoring of all aspects of performance of optical imaging systems, including linearity, gain, read noise, spatial resolution, and dark noise. Ideally, such a system would be compact, inexpensive, and stable. Optical imaging systems for use with small-animals are extremely sensitive, typically capable of detecting intensity values of less than 10,000 photons s−1 cm−2. On the other hand, much higher light intensities would be useful during setup and preview of the calibration device, facilitating real-time operation. For these reasons, the calibration system must be capable of providing light intensity values over an extremely broad range—typically over 7 orders of magnitude.